CONTENTS Inhalation- Definition Common conditions Advantages and disadvantages Inhalant drugs Types
Inhalation- Definition Inhalationis any drug or solution of drugs administered by the nasal or oral respiratory route. Inhalation(also known as inspiration) is the movement of air from the external environment, through the air ways, and into the alveoli.
Particle Size Mass median aerodynamic diameter <1μm: reach up to the alveoli, 0.5~5μm: beyond the 10th generation of bronchi (respirable particles), >5μm: oropharynx
Common conditions Inhalation therapy is a traditional treatment in chronic asthma and chronic bronchitis. Emphysema, Bronchiectasis
Advantages anddisadvantages Advantages: - Less systemic toxicity - More rapid onset of medication - Delivery to target of action - Higher concentrations available in the lung Disadvantages: - Time and effort consuming - Limitation of delivery device
Device Selections of device include： Nebulizer: small volume, large volume, ultrasonic Metered dose inhaler, MDI Dry powder inhaler, DPI Spacer Rotahaler spinhaler
Metered-dose inhalersA liquid propellantA metering valve that dispenses a constant volume of a solution in the propellant. Inhalationtechnique is critical for optimal drug delivery – only about 10% of drug reaches the lungs. Its also use with nebuhaler.
Metered-dose inhalers Fist be shaken to ensure that drug should be evenly distributed. Held upright and the cap is removed. Breathes out gently, but not fully With the mouth around the mouthpiece of the inhaler, the device is pressed to release the drug as soon as inspiration has begun. Inspiration should be slow and deep, be held for 10seconds if possible. Dose of inhalation will involve > 1 “puff” The length of time between inhalation is 15- 20 seconds.
Dry powder inhalers No propellant Breath-activated, and patient coordination is not as important an issue. The drug is formulated in a filler and contained in a capsule that is placed in the device and punctured to release the powder. Releasing drug on inspiration, require faster inspiratory flow rate Inspiratoryflow required depends on the resistance with in device.
Rotahaler Insert a capsule into the rotahaler , the coloured end first. Twist the rotahaler to break the capsule Inhale deeply to get powder into the airway Several breath may be required, does not required the coordination of the aerosol
Spinhaler It works similar to rotahaler, except that outer sleeve slides down to pierce the capsule and the propellor disperse the drug
Spacer Patient could not required coordinate inspirationa) Patient seals lips around the mouthpieceb) Depresses the actuatorc) The mist is trapped in the middle sectiona) Inhale without loosing the drug
Nebulizers Patient cooperation and coordination is not as critical It converts solution into aerosol particles, < 5μm. An acceptable time 5-10minutes. Two types: Jet nebulizers : Ultrasonic nebulizers Commercially available nebulizers deliver 12% to 20% of the nebulized dose into the bronchial tree.
Jet nebulizer With a jet nebulizer driving gas is forced through a narrow orifice. Thenegative pressure created around the orifice and it allows the smaller particles for inhalation and larger particles drop back into the reservoir
18 Some Disadvantages of Jet Nebulizers Less portable than inhalers Requires power source, maintenance, and cleaning Output is device dependent Delivery may take 5 to 10 minutes or longerO’Donohue et al. Chest. 1996;109:814-820; Dolovich et al. Chest. 2005;127:335-376; PulmicortRespules 0.25 and 0.5 mg [package insert]. Wilmington, DE: AstraZeneca LP, 6/2005. NAEPP.Publication no. 97-4051.
Ultrasonic nebulizers An aerosol can also created by high frequency(1- 2MHz) sound waves. Piezo-electric crystal causes ultrasonic vibrations, it will travel through liquid to the surface where they produce aerosol. Produce higher output than jet nebulizers Advantage- they operate quietly
Variable performance systems Small reservoirs and low gas flow (2- 15L/min) Shallow breathing less entrained room air, higher FiO2 Exhalation time variable filling of devices’ inspiratory reservoir Nasal cannula Oxygen mask Tracheostomy mask
Nasal cannula The proximity and size of the reservoir (NP/OP~50ml=1/3 of anatomic dead space) imply sensitivity to changes in inspiratory flow rate and particularly the loss of respiratory pause Flows>6L/min do not significantly increase FiO2>44% Drying of mucosa and epistaxis
Oxygen masks Reservoir volume= 150-250ml Re-breathing occurs at flow rates <4L/min Approx FiO2 0.4-0.6 Interferewith eating Easy displacement Increases aspiration by concealment of vomitus
Tracheostomy masks Delivery depends on presence of ETT and inflation status of its cuff Ifabsent or cuff is deflated, air from NP will mix with that being delivered to the tracheosotmy, furth er diluting the FiO2
Fixed performance systems Socalled because O2 delivery is independent of the patient factors outlined above Venturi-type masks Anesthestic breathing circuits
Venturi-type masks High flow oxygen delivery device Venturi modification of Bernoulli principle Jet of 100% oxygen through a fixed orifice, past open side ports, entraining room air FiO2 depends on size of side ports and oxygen flow Accurate FiO2 up to 0.5
Anaesthestic breathing circuits Closed system with valves (e.g. Ambu- bag) Reservoir volume = 600-1000ml Re-breathing at low flows (most require flows >150ml/kg) Theoretically capable of delivery FiO2 1.0 but practically ~0.6-0.8 due to sealing problem
Complications Barotrauma (middle ear and sinuses), gas embolism on decompression Oxygen toxicity Visual problem (myopia, cataract)
HumidificationA device to provide humidification of the air ways may be considered if either the normal means of humidifying the air ways or the mucociliary escalator are not functioning effectively. The upper air ways acts as a heat and moisture exchanger with the fully saturated expired gas giving up some heat and water to the mucosa. The epithelial lining of the airways from trachea to the respiratory bronchioles contains ciliated cells which are responsible for moving mucus proximally to the level of larynx.
Humidification Theefficiency of mucus transport is dependent on current functioning cilia and the composition of peri-ciliary and mucus layers. Viscosity of mucus is increased during bacterial infection Humidification has been shown to enhance tracheobronchial clearance
Humidification Conway (1992) hypothesizes that humidification by water or saline aerosol produces an increase in depth of the peri-ciliary and mucus layers, there by decreasing viscosity and enhancing the shearing of secretions by huffing or coughing. Humidificationmay be indicated to assist clearance of secretions when the clearance mechanisms is not optimally effective or when the normal heat or moisture exchange system of the upper airways is by passed by an endotracheal or tracheostomy tube.
Humidification Methods Systemic hydration – adequate humidification may be obtained by increasing the oral or intravenous fluid intake of the patient. Heat and moisture exchangers(HME) Nebulizer Steam inhalation
Hazards Inhalationof cold mist or water may cause broncho constriction in patients with hyper reactive air ways Water reservoirs may become infected Regulardisposal, disinfection or sterilization of all humidification equipment is essential to prevent infection.
References1. Cash’s text book, 4th Edition2. Physiotherapy for respiratory and cardiac problems, Jennifer A Pryor and Barbara A Webber, 3rd Edition3. Cardiopulmonary physical therapy, By: Elizabeth Dean, 3rd Edition4. Medical pharmacology, by: K D Tripathi, 4th Edition